The present invention generally relates to the field of electrochemical fuel cells and, in particular, to the utilization of organic materials, such as animal waste products, for the generation of electricity.
The annual accumulation of organic waste in the world is immense. For example, the annual accumulation of pig generated organic waste in Taiwan alone is estimated to be over 10 million tons. In addition to the need to address the environmental concerns associated with the disposal of such waste, it has been recognized that waste of this nature could be a valuable source of energy.
Much organic waste contains various substances that, when treated properly, can be converted to methane (CH.sub.4). Methane production by known biological treatment processes, such as anaerobic fermentation (also called anaerobic digestion), involves the conversion of organic matter to methane and carbon dioxide at modest temperatures, ambient pressures, and nearly neutral pH. Anaerobic fermentation is typically carried out in the absence of exogenous electron acceptors such as oxygen, nitrate, and sulfate through a series of microbial interactions. Conventional anaerobic fermentation is often used for waste water treatment.
Methanogens (i.e., methane-producing bacteria) have been studied for their utility in digestion processes for producing methane. Because of the limited number of substrates catabolized by methanogens, however, to degrade complex organic substrates to methane by anaerobic digestion, other organisms are necessary as well. A typical anaerobic digester, therefore, will normally contain a mixture of fermentative bacteria, acetogenic bacteria, and methanogenic bacteria.
Fermentative bacteria convert hydrolyzed polymers (soluble sugars, peptides, and long chain fatty acids) to organic acid and alcohol intermediates. These intermediates are then converted into hydrogen, carbon dioxide, and acetic acid by acetogenic bacteria, followed by conversion of the hydrogen, carbon dioxide, and acetic acid into methane by the methanogenic bacteria. The conversion of the acid and alcohol intermediates into methane is slow, relative to the rates of conversion of hydrogen and carbon dioxide into methane.
Presently, only a small percentage of the methane-generating potential of organic waste is extracted for energy use. Moreover, after the generation of methane by known processes, the remaining organic material typically takes the form of partially-treated compost which can be chemically unstable and biologically unsafe. This compost is currently used as an unsuitable fertilizer.
Additionally, biogas generated by the treatment of organic waste usually contains compounds other than methane, e.g., sulfur. In prior art systems, this sulfur must be removed from the biogas before the gas is introduced to an electrochemical converter, to avoid permanently damaging the converter. Thus, additional structure and components are required to purify the biogas prior to introducing the biogas to the electrochemical converter.
It is, therefore, the object of the present invention to provide systems and methods for converting to electricity organic material, such as animal waste, which is more efficient than known methods. It is another object of the invention to provide systems and methods that generate less pollutants than known methods. It is still another object of the invention to provide systems and methods for introducing unrefined biogas to an electrochemical converter.